It is known from experience to detect separately the torque for each of the two pedal cranks, respectively introduced into a bottom bracket by means of the two pedal cranks. It is also known, for detecting a torque acting on a shaft, to form a magnetized portion on the body of the shaft so that when applying or altering a torque, the magnetized portion alters its magnetization due to the magnetostrictive effect, which may be detected and evaluated by means of a magnetic sensor, for example by means of a coil, a Hall sensor or Reed sensor.
With regard to carrying out the measurement of torques in a shaft by means of the magnetostrictive effect, the correct positioning of the sensor relative to the magnetized portion of the shaft proves problematic. This difficulty increases further if, for a bottom bracket with a shaft and two pedal cranks connected to the shaft, the torque respectively introduced into the shaft is intended to be measured separately, for each of the two pedal cranks.
DE 10 2007 062 156.8, filed on 21 Dec. 2007, discloses a bottom bracket with a shaft formed as a hollow shaft, to which a first pedal crank and a second pedal crank are fastened, the shaft being configured either as an individual hollow shaft receiving both pedal cranks or as two hollow component shafts joined together fixedly in terms of rotation. In both cases, the chainring carrier is joined fixedly in terms of rotation directly to the hollow shaft and/or one of the two hollow component shafts. Such an arrangement proves disadvantageous as the chainring carrier has to be attached before installing the hollow shaft. If the shaft is formed by two hollow component shafts joined together, the assembly cost increases, as the two hollow component shafts still have to be additionally fastened together.